salt water storage

So I mixed some salt last Thursday, reef crystals. I have it stored in a 20 gallon brute container with a circulation pump and no heater. I was originally going to use it the next day but due to being busy and work I wasn't able to. Am I still able to use it for a water change? It's just fish...

I'm setting up a mixing station with two 65 gallon drums. I'm planning to do automated water changes using my Apex DOS. So the question that comes up is how do you store the salt-water? Do you keep it heated? Constantly mixing or an occasional run of the pump? Do you prefer to let it...